Experimental investigation of turbulence modulation in particle-laden coaxial jets by Phase Doppler Anemometry

Mergheni, Mohamed Ali; Sautet, Jean-Charles; Godard, Gilles; Ticha, Hmaied Ben; Nasrallah, Sassi Ben

doi:10.1016/j.expthermflusci.2008.11.004

Cited by 19 publications

(8 citation statements)

References 11 publications

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“…The weaker vortices will have little effect on the particles. However, if the Stokes number is much greater than 1, the momentum response time of the discrete phase is much greater than that of the time constant of the flow field and the discrete phase flow will pass through the turbulent vortices, although individual particles will show slight variations in their velocities because of a very small momentum exchange with the vorticies, as found by Mostafa et al [5] and Mergheni et al [6]. In this case, there will be transfer of turbulent kinetic energy to the fluid from the particles because the particles will create turbulent motion on a scale about their diameter, as suggested by Gore and Crowe [7].…”

Section: Introductionmentioning

confidence: 81%

“…Mergheni et al [6] investigated coaxial jet flows with 102-212 µm diameter glass spheres introduced in the central jet with two annular to central jet velocity ratios, 0.2 and 1.3. In the case of the slower central jet, the onset of a single peak mean axial velocity profile, indicating jet merging, was slightly beyond 10 nozzle diameters, the last profile reported.…”

Section: Introductionmentioning

confidence: 99%

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A Study of a Powder Coating Gun Near Field: Particle Flow in an Isothermal Staggered Concentric Air Jet

2014

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An experimental study of inert particle dispersion in an isothermal concentric air jet near field was conducted for cases of standard non-staggered and alternative staggered jet nozzles, each taken from a polymer powder flame deposition gun. The experimental work consisted of analysis of high speed digital images of the inert two phase isothermal jet flow, illuminated by a laser light sheet along and across the jet axis. The analysis of particle spread in the jet, represented by families of particle density distributions, clearly showed that the staggered nozzles resulted in a better-focused flow, with narrower distributions in the near field, and in the elimination of the recirculation zone that disrupted the particle flow in a non-staggered nozzle arrangement. In all cases, histograms of the cross-sectional particle area density were found to be approximately Gaussian. It was also found that there was a wide variation in the size and shape of the ground polymer particles used and these two characteristics caused a wide variation in the radial and axial velocities of the particles. Despite the differences between single-phase numerical simulations and experimental results, reported in Payne et al. [1], the introduction of particles into a numerical model produced satisfactory agreement with the particle velocities found experimentally.

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Section: Introductionmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

A Study of a Powder Coating Gun Near Field: Particle Flow in an Isothermal Staggered Concentric Air Jet

2014

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“…Vreman et al (2007) showed that there is another suppressing mechanism in inhomogeneous flows: the non-uniform relative velocity of the phases created because particles slip at the wall, collide, and slowly react with the continuous phase. Mergheni et al (2009) found that, near the injector at low Reynolds number, the presence of the particles dampens the gas-phase turbulence, while at higher Reynolds number, the gas-phase turbulence and the velocity fluctuation of particleladen jets are increased. Anand and Jenny (2009) presented a unified probability density function formulation for capturing the phenomena of turbulence modification of the continuous phase due to the dispersed phase turbulence, and gave the influence of gravity on the decay of the continuous phase Reynolds stresses.…”

Section: Introductionmentioning

confidence: 96%

Numerical Simulation of Turbulence Modulation by Cylindrical Particles in Round Jet

Lin

Shen

2014

Engineering Applications of Computational Fluid Mechanics

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In order to explore the turbulence modulation by cylindrical particles, the equation describing the probability density functions for the particle orientation, and the equations of Reynolds averaged Navier-Stokes, turbulence kinetic energy and turbulence dissipation rate with additional terms of particles are used and solved numerically in a round jet flow. The turbulence modulation at different axial distances from the nozzle exit in the initial region is given, and the effects of particle concentration, particle aspect ratio and Reynolds number on the mean streamwise velocity, turbulence kinetic energy and turbulent viscosity are analyzed for the particle mass concentrations ranged from 0 to 0.01%, Reynolds number ranged from 4000 to 13000, and particle aspect ratio ranged from 5 to 35. The results show that the critical parameter used to explain the increase or decrease of turbulent intensity caused by the addition of spherical particles is not suitable to explain the case of cylindrical particles. The particles injected in the flow have the effect of delaying the centerline mean axial velocity decay with increasing axial distance. This phenomenon is more obvious in the case of high particle concentration. The turbulence intensity enhancement caused by cylindrical particles is less downstream than near the nozzle exit. The cylindrical particle injection will enhance the turbulence intensity, and the degree of enhancement is position dependent and directly proportional to the particle concentration, Reynolds number and particle aspect ratio.

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“…Nezu and Azuma [6] utilized PTV method to simultaneously measure the velocities of solid and liquid phases in an open channel flow, and substantial turbulence enhancement was observed in the vicinity of the surface due to the particle movement. Mergheni et al [7] carried out experimental study on a vertical coaxial jet by PDA, from which the existence of particles was observed to reduce the velocity gradient in the shear layer, causing a decrease in turbulence intensity. In the recent simulation studies [8,9], the turbulence enhancement by large particles, as well as the turbulence attenuation by small particles have both been successfully predicted in a unified model by appropriate numerical settings.…”

Section: Introductionmentioning

confidence: 97%

Experimental study on the local turbulence modulation in a horizontal particle laden flow with rigid fence

Yang

Aoshima

Otakeguchi

et al. 2013

AIP Conference Proceedings

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The turbulence modulation by the existence of disperse phases, e.g. solid particles or liquid droplets, has attracted wide attentions in recent years. In this investigation, particles of different properties were fed with tracers into the turbulent atmospheric boundary layer disturbed by a rigid fence, and the velocities of both phases were obtained by PIV/ PTV methods respectively. From both ensemble average and instantaneous analysis, the presence of particles was found to attenuate the local turbulence around the fence and in the downstream. In this case, the induced sand dune erosion by the turbulence when installing the rigid fence is also expected to decrease. The influences of the particles follow the order: GH>GL>No.9. The Stokes number under the given conditions showed that all the particles under discussion should cause augmented dissipation of turbulence. Moreover, through analyzing the relative velocities between the two phases, the cross-trajectory effect was found to be another possible mechanism accounting for the observed turbulence modulation by the particles.

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Experimental investigation of turbulence modulation in particle-laden coaxial jets by Phase Doppler Anemometry

Cited by 19 publications

References 11 publications

A Study of a Powder Coating Gun Near Field: Particle Flow in an Isothermal Staggered Concentric Air Jet

A Study of a Powder Coating Gun Near Field: Particle Flow in an Isothermal Staggered Concentric Air Jet

Numerical Simulation of Turbulence Modulation by Cylindrical Particles in Round Jet

Experimental study on the local turbulence modulation in a horizontal particle laden flow with rigid fence

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